Automatic power position hold for control valves



Sept. 7, 1948. H. KIRKHAM AUTOMATIC POWER POSITION HOLD FOR CONTROL VALVES Filed Sept. 9. 194a M N m mink mzma OHM A Q PQ w? r H .d 4 m m f 0 OH Q 5 i5 8 J 5 E m OP f f -9 mw Q PH,

v I\ 7 WW 1| @N I N nw w w 0N HQ QM. g mnw\\ A; g jg: C W Qw nw 1 I P0 WEN v T\W mm 0 mm @8 o Gm QT mm M mm ON 0N I l mu 6 WWHOT NH Qfi OT PW 00 an Patented Sept. 7, 1948 AUTOMATIC POWER POSITION HOLD FOR CONTROL VALVES Hall Kirkham, Cleveland, Ohio, assignor to Bydraulic Control Engineering Company, Cleveland, Ohio, a corporation of Ohio Application September 9, 1946, Serial No. 695,680

11 Claims. (01. 277-20) This invention relates to valves for hydraulic hoist systems and more particularly to the socalled hoist and lower" or control valves for the operation of a hydraulic hoist supplied with high pressure liquid from the substantially constant volume pump.

It is the general object of the present invention to provide a novel and improved control valve for hydraulic hoists having incorporated therein mechanism for automatically retaining the valve in either of its hoist or lower positions, after it has been manually moved thereto, until motion of the hoist has substantially terminated, when the valve is automatically returned to its central or neutral position where free by-passing of the pump discharge to the reservoir is effected.

An important feature of the present invention comprises the arrangement of low pressure or discharge chambers in the valve housing arranged to selectively receive the liquid returning from the low pressure side of the hoist, together with low pressure relief valves permitting the discharge of this liquid from the chambers at a pressure adequate at all times to exert a holding force on the valve plunger in excess of that of the bias spring.

Another important feature of the invention consists in the provision of a bleed or by-pass for each low pressure relief valve to insure the return of the valve plunger to the neutral position under the action of its centralizing or bias spring.

Other and further objects of the invention will be more apparent to those skilled in the art upon a consideration of the accompanying drawings and following specifications wherein is disclosed for the sake of simplicity a single exemplary embodiment of the invention as applied to a relatively conventional hoist and lower valve, it being understood that the improvements, however, are applicable to various types and styles of valves for the same or similar purposes, without departing from the spirit of the invention.

In such drawing the single figure is a longitudinal central section through a hoist and lower valve and its reciprocable plunger wherein the housing is of the type adapted for immediate attachment to the reservoir or tank, permitting discharge of fluid directly to the same.

Many industrial and agricultural applications of hydraulic rams or hoists are provided with a more or less conventional double acting ram or hoist to which high pressure liquid from a constant volume pump, driven by a suitable prime mover, may be selectively delivered to either end bymeans of a hoist and lower or control valve,

which likewise handles the discharged low pressure liquid from the opposite end of the hoist, returning it to the tank or reservoir from which the pump takes its supply. In such combinations good engineering requires that when the valve is in the neutral or hold position it must by-pass the liquid from the pump directly to the tank at substantially zero pressure to relieve the load from the pump except when hoisting or lowering is actually taking place. To this end appropriate passages are provided in the valve housing and the plunger is biased to a central position from which it must be moved manually to achieve hoisting" or lowering, hereinafter called by the general term hoisting, meaning to actuate the hoist in either direction.

In a great many cases a plurality of hoists are used or other apparatus is associated therewith, requiring substantially simultaneous attention from the operator. It therefore becomes difllcult, if not impossible, for him to devote the time necessary for the full manipulation of the hoist, where he is required to hold the valve in an open or "hoist position until the full stroke of the hoist is completed. For the sake of economy the pumps are not always designed to provide rapid operation, thus requiring the operator's full attention to the control valve over a period of many seconds while he should be devoting his time to other controls.

The present invention contemplates making use of the flow of low pressure liquid returning from the inactive end of the hoist to hold the operating plunger in whatever position it has been placed by the operator, until the termination of the stroke of the hoist, when it is returned to its neutral or central position by any of the conventional devices, such as the well known centralizing spring.

In accordance with this invention the low pressure fluid returning from the hoist is so obstructed in its flow as to build up an adequate pressure to react on piston-like areas formed on the plunger to hold it in either of its hoist positions, whereby the operation of the device is substantially independent of the rate of, or changes in the rate of, flow of liquid returning from the hoist and yet full control of the valve is assured the operator in the event he desires to override the automatic holding means.

Referring now to the drawing, wherein the valve alone is illustrated, reference may be had to Patent No. 2,362,944, granted to W. T. Stephens, for Control valve for hydraulic system, for a general description of the valve and system. In the present instance the drawing shows at In a onepiece housing, preferably a suitable casting, ar-

ranged with mounting holes I 2 whereby it may be attached to a tank. A chamber l4 in the housing is provided with a port i5 to which high pressure liquid from a substantially constant volume pump is delivered during the whole time that the pump is in operation, which in the case of a tractor driven device is substantially during the whole operation of the tractor. The housing likewise contains a discharge chamber l6 and two waste passages I1 and i8, all connected to the tank by direct connections not shown and which, in other forms of valves, could be manifolded and piped to a suitable separate tank, as is common.

The housing is perforated from end to end by a cylindrical bore 20 closed by a hollow nut 2| at the left. This bore intersects the discharge chamber l8 and the arms 23, 24, of the high pressure chamber l4, which straddle chamber 16. It also intersects a pair of hoist ports 25, 26, adapted to be connected by suitable piping to opposite ends of the hoist cylinder. Near the ends of the housing are the low pressure chambers or pockets 2'! and 28, each connected by a passage 29, 30, respectively, to one of the waste passages I1, l8.

The cylindrical bore receives with a working flt a valve plunger 32 having a reduced diameter stem 33 extending out of the right end thereof and fitted with an eye 34 by which it may be manipulated. This reduced portion passes through a guiding bushing 35 forming the right hand wall of low pressure chamber 28, and an appropriate packing assembly 38 outboard of the blushing prevents leakage. At the left hand end the plunger is closed by flanged plug 31 which cooperates with a spring 38 whose opposite end bears on shoulder 39 on the plunger and 40 at the right wall of the low pressure chamber 21. The left end of the spring also bears against the inner end of cap 2| and thereby comprises a centralizing spring for resiliently holding the plunger in the neutral position shown, from which it may be moved manually to the left or right as will be later described.

The plunger is equipped with full diameter lands in symmetrical arrangement, including the short center one 42 and the widely spaced lands 43 and 44. In the neutral position the central land is submerged in chamber l6 while the outer lands 43 and 44 serve to isolate the hoist ports 25 and 26 thereby locking the fluid in both ends of the hoist and serving to hold it in any position in which it may be set.

In this central position the free by-passing of the high pressure liquid will be noted, for it passes through the deep grooves 45 and 45 in the plunger between the central land and the end lands and hence is able to pass through the bore in the walls 41 and 48 separating the chambers I4 and it. From l6 it returns directly to the tank.

Assuming the plunger to be manually moved to the left for its maximum stroke, it will be seen that land 42 closes off the bore in wall 41 while land 44 closes off the bore in wall 48, whereby chambers 14 and 16 are now isolated. High pressure liquid is then delivered through the radial openings 49 in the bottom of groove 45 in the plunger, enters the chamber 5| therein, presses open the check valve 53 and issues through the radial passages 55 in land 43 which now registers with hoist port 25. High pressure fluid is therefore delivered to one end of the hoist and moves it as required. Concurrently liquid is returned from the other end of the hoist and enters the hoist port 28 at the opposite end of the valve.

' This port is uncovered by land 44 and the passage of liquid into the low pressure chamber 28 takes place freely. Since this liquid is restricted in its discharge from chamber 28 the annular area 58 between the full diameter and the stem diameter of the plunger is exposed to this relatively low pressure acting toward the left. As long therefore as adequate pressure exists in chamber 28 the plunger will be held in its left hand position against bias spring 38 which, however, will act to return it to the central position when the pressure is sufilciently lowered in chamber 28, which happens when the hoist stops its movement, such as by reaching the end of its stroke or engaging some obstruction which it cannot overcome at the pressure of the fluid existing in it.

If the plunger had been pulled out to the right the operation just described would have been reversed, the flow taking place in corresponding passages, ports and bores in the opposite end of the plunger and housing which are substantial duplicates of those just described. It is not believed necessary to recount these flow processes here. With the plunger to the right the low pressure liquid returning from the hoist builds up a pressure in chamber 21 where it acts over the whole area of the end of the plunger. The flow is augmented to chamber 21 by a plurality of channels or grooves 6| by-passing the end of the spring.

In order to resist the flow of fluid from low pressure chamber 21 to the waste passage H by way of bore 29 or from chamber 28 to the corresponding waste passage l8 by way of bore 30, a spring pressed relief valve is provided for each. The arrangement is best shown at the left, where a hollow, internally threaded boss 63 receives a hollow threaded cap 65, the inner bore 81 of which forms a guide for the cuplike valve member 69, which seats at II at the junction of bore 29 and passage l1. A spring 13 of suitable weight urges the valve member 69 against its seat. This spring is adjusted, as will be later described, to provide an appropriate pressure in the low pressure chamber to insure holding the valve in the position to which it has been moved. Whenever the hoist stops moving there still remains trapped in that low pressure chamber, to which liquid is being returned, a quantity of liquid which would prevent the centralizing spring from returning the main plunger to neutral. To eliminate this difficulty a bleeder passage by-passes the valve plunger 69. Conveniently this will consist of a bore 15 leading to the interior of this plunger and a plurality of radial ports 11 opening into waste passage IT.

The spring pressed relief valves are provided toimprove the operation of the control valve under all conditions, and particularly in the event that the delivered volume of fluid varies. If instead of the relief valves fixed restricted orifices were provided, which could be designed or adjusted to take care of a known quantity of liquid, operation would be satisfactory as long as the volume of liquid always remained substantially the same. In the use of tractors, however, and other devices the engine may be operated at various speeds between idling and maximum, which produce a substantial change in the delivery volume of the pump. If the volume is reduced below that required to provide the proper pressure in chambers 21 and 28, the plunger will not remain in its operating position, while if the pressure becomes too great in extreme cases it Capacity 01' valve, 25 G. P. M, at zero pressure Pressure required in low pressure chamber 21 to keep plunger out, 40 p. s. 1.

Pressure required in 28 to keep plungerin, 100

p. s. i.

The pump used delivers 5 G. P. M. with the tractor engine idling and G. P. M. at full throttle. To obtain the desired results the bleeder port in check valve 69 is made of such a diameter that a pressure of 40 p. s. i. is required to force 5 G. P. M. through it. Corresponding valve plunger 10 has a bleeder port of such proportions that 100 p. s. i. is required to force 5 G. P. M. through it. Spring 13 is designed to allow opening-oi" 69 at 45 p. s. i., and the spring for plunger 10 is designed to permit its opening at 105 p. s. 1. They both give a minimum additional build-up of pressure when the valves are opened to allow the maximum fiow of G. P. M. Under these conditions, with the engine idling, sufllcient pressure will be built up in either of the low pressure chambers to insure the plunger being held in its operating positions. As the engine is speeded up and more liquid is delivered the pressure in the two chambers will become higher and the relief valves will be forced from their seats to allow the additional volume to be relieved. Due to the spring characteristics, however, the pressures in 21 and 28 will be only slightly increased during the entire delivery range of the pump and this increase will not prevent manual operation of the plunger should it be desired.

I claim:

i. A control valve for use between a pump, a tank and a double acting hydraulic hoist, in combination, a housing having two hoist ports and two low pressure chambers, a plunger reciprocable in said housing, resilient centralizing means for said plunger, each end of the plunger having an effective area exposed in one of said chambers whereby pressure therein exerts longitudinal effort on the plunger, means to connect one of said chambers to one of said ports when the plunger is manually moved in one direction and vice versa, a discharge outlet for each chamber and a spring pressed discharge valve for each outlet to resist flow therethrough.

2. A control valve for use between a pump, a tank and a double acting hydraulic hoist, in combination, a housing having two hoist ports and two low pressure chambers, a plunger reciprocable in said housing, resilient centralizing means for said plunger, each end of the plunger having an eiiective area exposed in one of said chambers whereby pressure therein exerts longitudinal eifort on the plunger, means to connect one of said chambers to one of said ports when the plunger is manually moved in one direction and vice versa, a discharge outlet for each chamber, a spring pressed discharged valve for each outlet to resist flow therethrough and a bleeder port for each outlet by-passing said discharge valve.

3. A control valve for use between a pump. a tank and a double acting hydraulic hoist, in combination, a housing having two hoist ports and two low pressure chambers, a plunger reciprocable in said housing, resilient centralizing means i'orsaid plunger, each end of the plunger having an effective area exposed in one of said chambers whereby pressure therein exerts longitudinal effort on the plunger, means to connect one 01' said chambers to one oi said ports when the plunger is manually moved in one direction and vice versa, a metered discharge outlet for each chamber and a spring pressed discharge valve for each chamber to resist flowtherefrom.

4. The control valve as defined in claim 3 in which the metered outlet is arranged directly in the spring pressed discharge valve.

5. In a valve of the type described, in combination, a bored housing, a grooved and landed plunger movable in said bore from a "central" to either of two hpist" positions, centralizing means for said plunger, a pressure inlet and a discharge in said housing communicating through plunger grooves in the "central position and isolated by plunger lands in either hoist position, two spaced hoist ports each with an adjacent chamber in said housing, said plunger having an eflective transverse area in each chamber facing the center, means including said grooves and lands to connect one hoist port to said high pressure inlet and the other to its adjacent chamber when the plunger is moved in a direction away from the adjacent chamber, an outlet for each chamber and a spring loaded valve resisting flow'through each outlet.

6. In a valve of the type described, in combination, a bored housing, a grooved and landed plunger movable in said bore from a "central to either of two hoist positions, centralizing means for said plunger, a pressure inlet and a discharge in said housing communicating through plunger grooves in the central position and isolated by plunger lands in either hoist position, two spaced hoist ports each with an adjacent chamber in said housing, said plunger having an eirective transverse area in each chamber facing the center, means including said grooves and lands to connect one hoist port to said high pressure inlet and the other to its adjacent chamber when the plunger is moved in a direction away from the adjacent chamber, an outlet for each chamber, a spring loaded valve resisting flow through each outlet and a bleeder passage by-passing each spring loaded valve whereby iull centralization is achieved.

7. In a control valve of the type described, in combination, a housing, a chamber therein for high pressure liquid, a pair of hoist chambers, a pair of low pressure chambers, a bore intersecting all of said chambers, a plunger operatively positioned in said bore and so constructed and arranged that in the central position the hoist chambers are isolated, and in either "hoist" position one hoist chamber is connected to the high pressure liquid chamber and the other to one of said low pressure chambers, an effective pressure area on each end oi said plunger in one of said low pressure chambers to be subjected to the pressure therein to hold the plunger in the hoist" position to which it has been moved, a resilient centering means for said plunger and a spring resisted discharge valve for each low pressure chamber to build up pressure therein when it receives liquid from a hoist port.

8. In a control valve of the type described, in combination, a housing, a chamber therein for high pressure liquid, a pair of hoist chambers, a pair 01 low pressure chambers, a bore intersecting all of said chambers, a plunger operatively positioned in said bore and so constructed and arranged that in the central position the hoist chambers are isolated, and in either hoist" position one hoist chamber is connected to the high pressure liquid chamber and the other to one of said low pressure chambers, an effective pressure area on each end of said plunger in one of said low pressure chambers to be subjected to the pressure therein to hold the plunger in the hoist" position in which it has been moved, a resilient centering means for said plunger, a spring resisted discharge valve for each low pressure chambet to build up pressure therein when it receives liquid from a hoist port and a bleeder by-pass for each discharge valve to permit functioning of said centering means.

9. In a hydraulic control valve, in combination, a housing having a high pressure inlet port, a liquid return port and two hoist ports, a plunger, resilient means to centralize said plunger, said plunger being manually movable to either side of center to connect one hoist port to the inlet port and the other to the liquid return port, means dependent on liquid flow between said last mentioned hoist port and return port to hold the plunger in the position set, in spite of said centralizing means, and spring pressed means to retard said flow.

10, In a hydraulic control valve, in combination, a housing having a. high pressure inlet port, a liquid return port and two hoist ports, a plunger, resilient means to centralize said plunger, said plunger being manually movable to either side of center to connect one hoist port to the inlet port and the other to the liquid return port,

means dependent on liquid flow between said last mentioned hoistport and return port to hold the plunger in the position set in spiteof said centralizlng means, spring pressed means to retard said flow and a small bleeder passage by-passing said spring pressed means.

11. A valve of the type described for use between a pump whose discharge varies between a predetermined minimum and a maximum, a tank and a double acting power cylinder; comprising in combination,a housing having a bore, a plunger reciprocable in said bore between a central and either of two power" positions and having lands and grooves, means biasing said plunger to central" position, a pressure inlet chamber and a discharge chamber in said housing communicating through plunger grooves in the central position and isolated by lands in either power position, two spaced power ports each with an adjacent pocket in said housing and each port and pocket intersected by said bore, said plunger having an effective transverse area in each pocket, means including said grooves and lands to connect one power port to said high pressure inlet chamber and the other to its adjacent pocket when the plunger is moved to "power position, an outlet from each pocket to said discharge chamber, a, spring loaded valve resisting flow through each outlet, and a bleeder passage by-passing each spring loaded valve, each passage being calibrated to pass the minimum flow from the pump at substantially the pressure required on the corresponding transverse area to overcome said plunger biasing means.

HALL KIRKHAM. 

